Cathode ray storage tube having storage target with surface grooves and dielectric film overlying the grooves



Apnl 23, 1968 N. J. KODA ETAL 3,379,914

CATHODE RAY STORAGE TUBE HAVING STORAGE TARGET WITH SURFACE GROOVES AND DIELECTRIC FILM OVERLYING THE GROOVES Filed Feb. 1, 1966 Fig. l.

Nobuo J. Kodu Leon S. Yoggy,

INVENTORS.

ATTORNEY.

United States Patent CATHODE RAY STORAGE TUBE HAVING STOR- AGE TARGET WITH SURFACE GROOVES AND DIELECTRIC FILM OVERLYING THE GROOVES Nobuo J. Koda, Vista, and Leon S. Yaggy, North Carlsbad, Califi, assignors to Hughes Aircraft Company,

Culver City, Calif., a corporation of Delaware Filed Feb. 1, 1966, Ser. No. 524,298

8 Claims. (Cl. 31389) ABSTRACT OF THE DISCLOSURE The invention relates to cathode ray tubes and particularly to the type of cathode ray tube utilizing a storage target offering high storage pattern resolution and thereby improving the operation of that type of tube known as a scan conversion tube.

Conventionally, a storage cathode ray tube comprises an evacuated envelope having a storage target positioned at one end thereof. An electron gun is provided at the other end of the envelope and offers a source of electrons to form an electron beam for impingement on the target. Means are provided which are responsive to signals to be stored on the target for modulating the produced beam and provide on the target surface a charge storage pattern relating to the external signals. In this mode of operation the beam is denominated a writing beam. A collector electrode may be positioned adjacent the target and may be operated to capture electrons in relation to the charge pattern existent 0n the target. In this operation, which may be a reading operation, the electron beam is divided into two portions, one of which may pass through or be captured by the target and the other of which may be collected by the electrode in some direct relation to the storage pattern on the target surface.

Alternately, and as will be hereinafter described in detail, the electron gun may have associated therewith in close physical juxtaposition an electron multiplier. Thus, when the gun is used in its reading mode the electron beam provided is divided into two portions as it approaches the target surface, one portion of which will be captured by the target and the other portion of which will be returned to the multiplier to provide thereat an output signal again directly related to the charge pattern that has been positioned on the target surface.

As will be understood by technical people familiar with this field, storage targets have conventionally been constructed of electroformed metallic mesh havin a storage dielectric evaporated on one surface thereof. With this type of prior art storage target meshes have been constructed which provide up to approximately 1500 target elements per inch. With such target structures it has been found that charge pattern resolution and tube writing and erasing speed have not been at the optimum level desirable in certain service applications.

With the above in mind, it is a general object of the invention to provide, in combination with cathode ray tube structure noted above, a storage target that will offer an improved degree of charge pattern resolution as compared to prior art arrangements.

It is yet another object of the invention to provide 3,379,914 Patented Apr. 23, 1968 ice a storage target structure again, in combination with the noted general arrangement, offering low capacitance characteristics as compared to prior art structures and thereby importantly improve both the writing and reading speeds of tube operation.

It is a specific object of the invention to provide, as an article of manufacture, a storage target structure offering the advantages and improvements noted above and which may provide as many as 5000 target elements per inch.

These and other features and advantages of the invention will be more clearly understood by reference to the following specification and the related drawings, wherein:

FIGURE 1 is a diagrammatic illustration of a cathode ray tube incorporating the invention; and

FIG. 2 is an enlarged segmented view of a preferred storage target structure.

Describing the invention in detail and directing attention to the figures, the numeral 10 generally indicates a typical cathode ray tube structure comprising an evacuated glass envelope 12 having an enlarged forward portion 14 with a storage target indicated generally at 16 located therein.

An electron gun 18 which may be of the conventional image orthicon type or an improved version thereof is positioned at the opposed end of the envelope 12 and aligned with the target 16. An electron multiplier schematically illustrated at 20 of conventional form, is positioned in close juxtaposition to the electron gun 18. The gun 18, of course, is arranged to provide a pencil-like electron beam as will hereinafter be described in detail. Electrical lead 22 is attached to the output signal electrode of the multiplier 29 and provides a mode of signal pickup in the conventional manner.

As is well known in the art the electron beam produced by the gun 18 may be properly aligned, focused and de flected by either electrical fields or magnetic fields. For purposes of this disclosure, it will therefore be understood that an alignment coil 24 may surround the envelope 12 in the area of the gun 18 and a focus solenoid or coil 26 may be positioned to surround the envelope 12 to act in an electrical lens capacity to provide beam focus on the target surface. To assure accurate beam scanning over the target surface in raster fashion, a deflection coil 28 and shading control ring 30 are provided. A collector electrode 32 of conventional form is positioned adjacent and parallel to the target 16 and is provided with a lead 34 extending externally of the envelope 12 whereby the electrode may be utilized in one form of tube operation to act as a pickup for output signals related to the storage charge pattern.

Directing attention to FIG. 2 which is a fragmentary enlarged and sectioned view of a preferred form of the storage target, it will be understood that the target comprises an imperforate metallic backing plate 36 having the surface thereof grooved as at 38, 38, said grooves defining a plurality of apices 40, 40 disposed over the entire surface of the plate 36. While the grooves are here shown as uniform and of triangular configuration, as seen in cross-section, it will be understood that other geometric configurations may be utilized within the contemplated scope of the disclosed invention.

The target structure additionally comprises a relatively thin dielectric film 41 adhering to the grooved surface of the backing plate 36 and physically abutting the latter at the apices 40 to define with the backing plate empty cavities with the surface of the grooves 38. At the points of contact, namely, the apices 40, the dielectric film 41 is provided with discrete segments of diffused electronically conductive material such as metal 42 which penetrate the film 41 and expose, on the surface thereof, an electrically conductive path to the backing plate 36. The

metallic paths 42 may be formed of diffused gold as hereinafter described.

A suggested method of constructing the type of target here under consideration may involve providing a metallic backing plate of desired material such as nickel and forming the grooves or cavities 38 therein utilizing a conventional photo-resist and acid etch method. If such a mode of construction is employed, it has been found that grooves 38 may be formed in the plate 36- up to approximately 5000 grooves per linear inch which is substantially greater than the 1500 meshes per inch of the prior art electroformed targets.

After grooving the plate 36, the grooved surface thereof may have a thin film of metallic gold evaporated thereon. To provide a base for dielectric film positioning, an extremely fine or thin plastic sheet is formed and positioned, in planar fashion, over the apices 40 of the backing plate 36. One mode of providing this plastic film is to use a plastic known as collodion and forming the thin film by placing a droplet thereof in liquid form on the surface of another liquid such as water. The plastic collodion then forms a thin film on the second liquid surface and the film is positioned across the apices 40 of the backing plate 36.

Thereafter, a thin film of dielectric is deposited by vacuum evaporation on the plastic collodion film so that the apices 40 support the dielectric film 41 in the manner shown. An appropriate dielectric has been found to be zinc sulfide, although other materials may be utilized.

After dielectric positioning, the target 16 is subjected to a baking operation which unites the backing electrode 36 and the dielectric film 41, destroys the plastic collodion film and causes the gold theretofore deposited on the apices 40 to diffuse through the dielectric film 41 and provide the electrically conductive paths 42. In this manner a target structure is constructed having the dielectric film 41 defining with the backing electrode 36 a multiplicity of evacuated cavities or grooves 38. In the assembled tube a signal output lead 37 may be connected to the backing electrode 36.

It will thus be understood by those skilled in the art that a target 16 of this construction substantially increases the discrete number of storage elements over the target surface. Additionally, it has been found that the target structure so formed has substantially lower capacitance than comparable prior art targets olfering the advantage of improved tube operation, to wit, a higher degree of storage charge resolution and substantially increased speed of tube operation in both the writing and erasing mode.

In the operation of a cathode ray tube incorporating the invention the cathode of the electron gun 18 may be initially held at a desired reference potential, for example, ground, and the dielectric film 41 may be stabilized at a slightly negative potential by impingement of the electron beam thereon. To accomplish this, the backing plate 36 may be raised in a positive direction to a potential which is somewhat below the first secondary emission crossover point for the dielectric material 41. The electron beam produced by the gun 18 then scans the target 16 by appropriate operation of the deflection coil 28 and as a result of the negative charges of the electrons which are deposited, the material 41 becomes stabilized at approximately the potential of the cathode. Thereafter, the potential of the backing electrode 36 is returned to zero or ground and as a result of the capacitive interlock between the backing plate 36 and the film 41 the latter is reduced to a somewhat negative potential.

To initiate the writing mode of operation the energy of the electron beam is brought to a value in excess of the noted first cross-over point by raising the target potential so the film 41 is above the first cross-over and the beam is scanned on the target in raster fashion and modulated by an input signal related to the charge which is desired on the film 41. As the beam strikes the film 41 secondary electrons escape therefrom and may be collected by the electrode 32 and discrete segments 42 of the target 16 The bombarded regions of film 41 are positively charged to potential levels corresponding to an input signal modulation of the beam and therefore a charge pattern corresponding to the signal is set up.

When it is desired to non-destructively read the stored information a constant current beam is produced by the gun 18 and again the target 16 is scanned while said target is held to a potential of about zero to 25 volts. As the electrons in the beam approach the written discrete segment of the dielectric film 41, some are permitted to strike and be captured by the conductive paths 42, since some of the negative repelling charges were removed from the film during writing. The unwritten discrete segments of the dielectric film 41, of course, repel the electrons in the constant current beam and they may be proportionately divided and captured by the electrodes 32 and conductive paths 42 creating an output signal via lead 34 corresponding to the charge pattern on the dielectric film surface 41. In another mode of operation, the repelled electrons may be returned to the electron multiplier 20 and an output signal may be obtained at the multiplier via leads 22 again directly related to the charge pattern on the surface of the target 16. It will also be apparent to persons familiar with scan conversion tubes that an output signal may be obtained at the backing electrode 36 via lead 37.

It has been found that the operation of a cathode ray tube incorporating the target structure defined provides a high degree of output signal resolution as a result of the excellent resolution of the charge pattern on the target surface. The relatively low capacitance offered by the target structure enables the tube to be operated at substantially increased writing and erasing speeds as compared to prior art scan conversion tubes. Additionally, signals of one frequency may be used to create the storage pattern on the target surface and the readout mode of operation may be at a different frequency where a service application so requires.

The invention as shown is by way of illustration and not limitation and may be modified within the scope of the appended claims.

What is claimed is:

1. In an electronic storage tube for storing input signals and providing output signals corresponding to the input signals,

an envelope,

an electron gun to create an electron beam at one end of the envelope for time-shared operation between the erasing, writing and reading mode,

a storage target at the other end of the envelope including,

an imperforate metallic plate,

said plate having a multiplicity of cavities on a side thereof facing the gun,

said cavities having disposed therebetween a plurality of apices, and

a thin relatively planar dielectric film disposed on said plate side and physically engaging said apices and defining evacuated spaces with the surface of the cavities.

2. An electronic storage tube according to claim 1, and including electrically conductive paths penetrating the film and electrically contacting the apices.

3. An electron storage tube according to claim 2, wherein said cavities are in the form of grooves and are uniform as seen in cross-section.

4. An electron storage tube according to claim 3, wherein said grooves are triangular as seen in cross-section.

5. In an electron storage tube for storing input signals and providing output signals corresponding to the input signals,

an envelope,

an electron gun to create an electron beam within the envelope,

a storage target at the other end of the envelope including a metallic backing plate,

said plate having a plurality of cavities on one side thereof defining a plurality of apices intermediate the cavities,

a generally planar dielectric film disposed on said plate and physically contacting the apices,

electrically conductive paths penetrating the film and contacting the apices,

said film in the discrete segments thereof intermediate the apices being in spaced relation to the backing plate,

and means within the envelope for collecting electrons repelled from the target surface during tube operation.

6. An electronic storage tube according to claim 5, wherein said last-mentioned means comprises an electron multiplier adjacent the gun.

7. An electron storage tube according to claim 5, wherein said last-mentioned means comprises an electrode im mediately adjacent the target.

8. As an article of manufacture a storage target for use in a cathode ray tube capable of accepting and retaining an electric charge pattern thereon, said target comprising a metallic backing plate having a plurality of cavities uniformly distributed over the surface of the backing plate and of generally uniform configuration as seen in sectional view, said cavities being formed on one surface of the plate, interposed apices separating the cavities, an electrically chargeable dielectric film of substantially planar configuration positioned on said one surface of the plate and engaging the apices, the film intermediate the apices being in spaced relation with the surface of the cavities, and electrically conductive paths penetrating the film and electrically contacting the respective apices.

References Cited UNITED STATES PATENTS 2,601,452 6/1952 Pensak 3l389 X 2,617,058 11/1952 Boer et al. 3l389 X 3,201,630 8/1965 Orthuber et a1. 313--89 X 3,258,892 7/1966 Rushton 52-615 JAMES W. LAWRENCE, Primary Examiner.

V. LAFRANCHI, Assistant Examiner. 

